Magnetic core



Patented Nov. 1, 1927.

UNITED STATES PATENT OFFICE.

VICTOR E. LEGG, OF MON'I'CLAIR, NEW JERSEY, ASSIGNOR TO BELL TELEPHONELAB- ORATORIES, INCORPORATED, OF N EW'YORK, N. Y., A CORPORATION OF NEWYORK.

MAGNETIC CORE.

Application filed January 3, 1927. Serial No. 158,802.

This invention relates to electrical insulation and more particularly tothe insulation of the particles used in the manufacture of magnetic dustcores. I

' Magnetic dust cores are being extensively used as cores for loadingcoils to improve the transmission characteristics of signaling lines.nickle and iron are now replacing iron to a considerable. extent forthis purpose. These alloys, when formed into cores and properly heattreated, are peculiarly desirable for loading coil cores by virtue ofproperties, some of which vary when the alloy material is strained, asis incidentally done by changing its form in compressing the dust intosolid cores. It is, therefore, best to perform the heat treatment afterthe dust has been compressed into core form. Furthermore, it isnecessary to insulate the individual particles prior to the core formingoperation, to reduce eddy current losses in the completed core. It istherefore necessary to provide an insulation which will withstand themechanical pressures used in forming the core and the high temperatureemployed in the heat treatment.

In accordance with this-invention the material used to produce theinsulating coating on the magnetic dust is lead sesqui-oxide Pb O orother oxygen bearing material which Will liberate some of its oxygen ator somewhat below the temperatures employed in the'heat treatment of thecores. During the heat treatment oxygen is released and combines withthe magnetic material to produce an oxide thereof in the form of acoating on the particles, the residueof the oxygen bearing materialbeing another form of lead oxide, or other non-conducting substance ifthe original material is other than a higher oxide of lead.

In another aspect the invention is a method of preparing magneticstructures an d more particularly magnetic dust cores. As applied tocores, for example, this method, specifically stated, comprises coatingeach particle of a mass of the magnetic dust with an oxygen bearinginsulating substance which will release part of its oxygen at a definitetemperature, preferably an oxide, for instance, lead sesqui-oxide b 0compressing the coated particles into a solid core, and heat treatingthe core to improve the magnetic properties of the core material.

Certain magnetic alloys containing An advantage of this method is thatonly a single heat treatment is necessary to form the double insulatingcoating on the par ticles and to improve. the magnetic properties of themagnetic alloy material.

A more detailed description of the invention follows, and theaccompanying drawing illustrates one embodiment of the invention, Fig. 1being a perspective view of a single magnetic ring and Fig. 2illustrating a plurality of rings combined to form a magnetic core.

In carrying out the present invention the magnetic material ispreferably prepared from an alloy containing nickel and iron. Apreferred form of alloy contains 78 nickel and fil iron. For adescription of this and other alloys which may be used as core materialsee patent to G. W. Elmen, No. 1,586,884, issued June 1, 1926. Obviouslyother alloys may also be used. The magnetic alloy, which may be in slabform is reduced to a finely divided form, such as a fine dust, in anywell known manner, as for example by crushing in a hammer mill or othersuitable reducing apparatus, and is subsequently rolled in a ball mill.The dust is sieved and the portion passing through a 120 mesh sieve isused for core-material. This dust is mixed with a material to coat theparticles and pressed into core form. The coating. material preferablyconsists of a higher oxide, for instance, lead sesquioxide, Pb O whichis mixed with the dust, the weight of the oxide being approximately 5%of that of the alloy dust. Other materials may be used instead of leadsesquioxide with equally good results. Such materials may consist ofmanganese dioxide, MnO nickel sesqui-oxide, Ni O antimony pentoxide, $100 or bismuth oxide, Bi O The magnetic dust is mixed with the leadsesqui-oxide to insure a thortmgh coal ingon the individual particles. Amass. of: the coated particles isthen placed in a mold and compressedinto "core rings, such as is shown in Fig. 1, with a pressure ofapproximately 200,000 pounds per square inch.

The compressed'core rings are then transferred to an electric oven andgiven a heat treatment to increase the permeability of the magneticmaterial or otherwise improve its magnetic properties. This treatment iscarried on at temperatures between approximate- 1y I" C. and 550 C. andthe rings are thereafter cooled. During the heat treatment the leadscsqui-oxide liberates oxygen at approximately 370 C. and at somewhathigher temperatures this oxygen combines with the nickel and iron toform an insulating coating of nickel and iron oxides on the individualparticles and there is left a lead oxide residue, which is alsonon-conducting, as a secondary coating on the insulated particles of themass. Such an insulating coating is chemically inert and stable at themaximum temperature of the heat treatment and will not break down tocause deleterious changes in the permeability of the magnetic materialobtained by the heat treatment. For a detailed account of heattreatments employed with nickel iron alloys, reference is made to atentsof G. W. Elmen, No. 1,586,884 an No. 1,586,889, issued June 1, 1926.

When a core is to be made, in accordance with this invention, for atelephone loadin coil, a plurality of these rings are stacke coaxiallyto form a complete core as shown in Fig. 2, on which the usual toroidalwinding is applied, the number of rings used depending u on the existingelectrical charac teristics o the telephone circuit with which theloadin coils are to be associated.

Althoug the above described method is preferred in forming the corerings, due to the advantage of forming the double coating of insulatingmaterial during the heat treating process, it is within the scope ofthis invention to subject the coated particles to heat treatment priorto forming the core rings, to change the nature of the insulatingcoating on the particles. Metallic structures other than ma etic coresare also within the scope of t e invention.

What is claimed is:

1. A metallic structure comprising magnetic material in the form ofdust, a property of said material being improved by heat treatment, andan insulating coating on the dust particles comprising an oxide of saidmaterial and a lower oxide of another material which forms a higheroxide, which latter is reducible to the lower form of oxide at atemperature at least as low as that employed in said heat treatment.

2. A magnetic structure comprising magnetic dust of an alloy consistingchiefly of nickel and iron, a property of which is improved by heattreating at a temperature in the range between 450 C. and 550 C., and aninsulating coating on said dust particles comprising oxides of nickel,iron and lead.

3. A magnetic structure comprising elements of magnetic material, aproperty of which is improved by heat treatment and which oxidizes atthe temperature of said heat treatment, and an oxygen bearing substanceseparating said elements which releases oxygen at a temperature at leastas low as that employed in said heat treatment, whereby when thestructure is heat treated oxygen will be released and an insulatingoxide of the magnetic material will be formed between the elements.

4;. A magnetic structure comprising a mixture of particles of magneticmaterial, properties of which are improved by heat treatment and whichoxidize at the temperature of said heat treatment, and an oxygen bearingsubstance which releases oxygen at the temperature employed in said heattreatment, whereby when the structure is heat treated oxygen will bereleased and an oxide of the magnetic material formed.

5. A magnetic structure comprising a mixture of particles of an allocontaining nickel and iron, properties of w ich are improved by heattreatment and which oxidize at the temperature of said heat treatmentand an oxygen bearing substance which releases" oxygen at thetemperature employed in said heat treatment, whereby when thestructureis heat treated oxygen is released and nickel and iron oxidesare formed.

6. The method of producing a magnetic structure from magnetic dust, apropert of which is improved by heat treatment, w ich method comprisesmixing the dust with a substance which liberates oxygen when heated at atemperature at least as low as that employed in said heat treatment andsubsequently subjecting the mixture to said heattreatment.

7. The method of producing a magnetic structure from magnetic dust, apropert of which is improved by heat treatment, w ich method comprisesmixing the dust with a substance which liberates oxygen when heated at atemperature at least as low as that ing said dust into a self-sustainingsolid, and subjecting said solid to said heat treatment.

8. The method of producing a magnetic structure from magnetic elementswhich comprises assembling said elements into the desired structuralform with an oxide therebetween, causing said oxide to release oxygenand leave a non-conducting residue and causing said oxygen to unite withthe magnetic material to form a non-conducting oxide.

9. The method of producing a magnetic structure from elements of analloy consisting chiefly of nickel and iron, a property of which isimproved by heat treatment, which method comprises assembling theelements with an oxide therebetween and subjecting the structure to saidheat treatment, thereby causing said oxide to liberate oxygen, leaving anon-conducting residue, and causing said liberated oxygen to unite withthe magnetic material to form a non-conducting oxide.

10. The method of producing a magnetic employed in said heattreatment,compressstructure from magnetic dust of an alloy consisting chiefly ofnicklel and iron, a property of which 'is improved by-h eat treat ment,which method comprises mixing the dust with an oxide, compressing salddust into a self-sustaining solid and subjecting said solid to said heattreatment, thereby causing saidoxide to liberate oxygen, leaving aresidue of non-conducting substance,

and causing said liberated oxygen to'unite with the magnetic dust toform a non-conat a temperature in the'r'ange between 450 C. and 5509 C.which method vcomprises mixing said dust weight of the oxide beingapproximately 5% of the weight of the dust, subjecting the mixture tohigh pressure to form a homogeneous solid, and heating said solid .at a

temperature within said range whereby said 'lead 'sesqui-oxide ischanged to lead oxide and'the released oxygen is' caused to unite withthe nickel and iron to formoxides thereof.

In witness whereof, I hereunto subscribe my name this 30th day ofDecember A. D;

VICTOR E. LEGG.

with lead sesqui-oxide, the

